Characterization of dermatologic changes in geriatric rhesus macaques

Nonhuman primates are frequently used for aging studies. We observed a high prevalence of skin disease among a group of geriatric rhesus monkeys (mean age = 25 years; n = 9) used in aging behavioral studies. Gross and histopathologic changes in the skin of these geriatric rhesus were compared with skin from control adult monkeys (mean age = 10; n = 4) and sun-exposed monkeys (mean age = 11; n = 4) to characterize age-related skin changes. Biopsy specimens were taken from four specified skin locations (lateral to bridge of nose, ventral midline, dorsal midline, perineal area) and from additional areas where skin lesions were present. Samples were routinely processed and evaluated by light microscopy. Blood samples were collected and tested for estrogen, thyroid-stimulating hormone, triiodothyronine, thyroxine, and cortisol levels. The axilla was swabbed and samples were obtained for bacterial culturing. All nine of the geriatric monkeys had notable dermal lesions, while one of the control monkeys and one of the sun-exposed monkeys had abnormal findings. Major gross findings included increased areas of erythematous skin, wrinkling, focal skin scaling, thinning of hair, foot calluses, and exudative lesions. Histologic skin changes included subacute dermatitis, acanthotic dermatitis, and a lesion resembling an early solar lentigo in the sunexposed animal. These changes were not associated with hormonal abnormalities or bacterial pathogens. Histologic changes are compatible with nonspecific skin changes observed in elderly humans. This study establishes a baseline of dermatologic changes of the aging rhesus macaque.